1. Field of the Invention
This invention relates to an electric switch device incorporating a device for monitoring the lifetime of the switch device during its operation and for notifying the time for its maintenance and inspection.
2. Prior Art
FIG. 1 shows an electromagnetic contactor which is a typical example of electric switch devices. A fixed contact 1 is mounted on one end of a fixed contact element 2, and a terminal screw 3 is connected to the other end of the fixed contact element 3. A movable contact 4 is mounted on a movable contact element 5 and is disposed in opposed relation to the fixed contact 1. The movable contact element 5 is supported on a movable contact element-supporting member 6 which is mounted on a movable core 7. The movable core 7 is adapted to be attracted by an electromagnet constituted by a fixed core 9 and a coil 10 and is adapted to be returned by a return spring 11, the fixed core 9 being mounted on the bottom of a casing 8 within which the movable core 7 is mounted. Reference numeral 12 denotes a contact spring, and reference numeral 13 denotes a distal end of the movable contact element-supporting member 6 projecting exteriorly of the casing 8 through a hole 14 formed through the casing 8. The distal end 13 is used for operation-indicating purposes, and also can be used to guess the lifetime of the electromagnetic contactor from the amount of projection of the distal end 13.
For opening and closing this electromagnetic contactor, a switch element (not shown) is closed to supply electric current to the coil 10 through an electric power source which is connected serially to the coil 10. As a result, the fixed core 9 is magnetized to attract the movable core 7, so that the movable contact element-supporting member 6 descends against the bias of the return spring 11. As a result, the movable contact 4 is brought into contact with the fixed contact 1 to thereby close the electromagnetic contactor. At this time, the contact spring 12 is compressed by the movable contact element-supporting member 6 to push the movable contact element 5 so as to urge the movable contact 4 against the fixed contact 1. When the electric current to the coil 10 is interrupted, the movable core 7 is moved upwardly under the bias of the return spring 11, so that the fixed contact 1 is spaced apart from the movable contact 4, thereby opening the electromagnetic contactor.
In an electric switch device such as an electromagnetic contactor, in order to know whether the consumption of the contacts reaches a limit when the contacts are fused, dissipated and consumed by the energy produced by its opening and closing operations, this has conventionally been done by periodically removable the contact elements and checking the appearance thereof, or by a method of measuring a so-called wipe amount in which the electric switch device can be still used even when the contacts are worn. However, the lifetime can not be accurately determined by checking the external appearance with the naked eyes. Therefore, there has been proposed another method in which as shown in FIG. 1, the distal end 13 of the movable contact element-supporting member 6 is adapted to project outwardly through the hole 14 formed through the casing 8, and the amount of consumption cf the two contacts 1 and 4 is guessed by viewing the amount of projection of the distal end 13 when the two contacts 1 and 4 are held in contact with each other.
There has been known that the lifetime of the contacts depends on the frequency of their opening and closing operations. However, if the inspection is periodically carried out, the frequency of the opening and closing operations during such a period is not always constant, and the time for such inspection can not be grasped quantitatively. Therefore, in another conventional method, a photoelectric switch is used for detecting the movement of the movable contact element 5. Each time the electromagnetic contactor is opened and closed, the light applied from a light-emitting portion of the photoelectric switch to its light-receiving portion is interrupted by a light shield plate mounted on the movable contact element-supporting member 6, and the frequency of such interruption is counted by the light-receiving portion, thereby determining the time for the inspection of the lifetime of the electromagnetic contactor. However, the former method has a problem that the visual inspection of the amount of projection of the distal end 13 is not precise. The latter method also suffers from the drawback that the use of the photoelectric switch makes the device complicated.